The Impact of Struvite and Soil pH on Chilli Pepper Plant Growth and Nutrient Release

Struvite (MgNH4PO4⋅6H2O), a sustainable and highly efficient slow-release fertiliser, is gaining 442 significant attention as a promising solution for nutrient recovery from waste streams. Its unique composition, which includes essential nutrients like nitrogen (N) and phosphate (PO4), makes it an effective alternative to conventional fertilisers. In contrast, the widespread application of traditional NPK fertilisers often leads to a high loss of nutrients in the soil through leaching and runoff, negatively impacting both plant growth and overall soil health. While struvite has shown high efficacy in cultivating various crops, its specific effectiveness for growing chili pepper plants and its nutrient leaching behaviour in tropical soil environments have not been extensively studied. To address this knowledge gap, a comprehensive 60-day pot trial was conducted, comparing struvite with conventional NPK fertiliser. The experiment used twelve pots with different soil pH levels, treating them with three fertiliser types at two different dosages, along with a control group. The study, conducted outdoors under shade, revealed that struvite applied at a higher dosage in alkaline soil (pH up to 8.5±0.05) significantly enhanced plant growth compared to NPK treatments, achieving a maximum plant height of 33.4±2.0 cm, a plant body weight of 23.6±2.1 g, and a high leaf count of 57±3.0 leaves. While NPK fertilisers also performed better in alkaline soils, they did not match struvite's performance. Critically, the study confirmed that struvite provides a more controlled and gradual nutrient release than NPK. For instance, the highest PO4 release rate for struvite was 510±10.0 mg/L on day 25 under acidic conditions, while in alkaline soils, its release was slower and more sustained, peaking at approximately 250 -290±5.0 mg/L. These findings highlight the potential of struvite as a viable and sustainable alternative to conventional fertilisers, contributing to reduced nutrient runoff, supporting circular economy practices, and ultimately improving long-term soil health.